The best interests of the insurance company ARE NOT ALWAYS the same as YOUR best interests. You should try to obtain a policy with a “consent to settle” clause which requires the carrier to obtain your written permission to settle a claim against you. If not, the carrier can settle a claim that you believe is very defensible without your permission.
A “hammer” clause is one in which the insurance company must obtain your written permission to settle a claim against you BUT YOU ARE RESPONSIBLE for all costs exceeding the amount of the settlement proposed by your carrier if you will not agree to that settlement. If you push the case to trial and you win — you avoid having the proposed settlement becoming a permanent part of your claims history. But if you lose — you will have to pay the difference between the amount of money the case could have been settled for and the actual costs of awards and extra defense.